A fungal toxin is a secondary metabolite secreted by a toxin-producing fungus and a natural toxic compound capable of causing various injuries on the human being and the livestock. Among fungal toxins ever found, aflatoxin (hereinafter referred to as “AFT”) is the most toxic fungal toxin, and its toxicity, carcinogenicity and contamination frequency all rank the first among biological toxins. Sterigmatocystin, i.e., ST, is a precursor for aflatoxin synthesis and produced mainly by the fungi such as Aspergillus versicolor, Aspergillus flavus, Aspergillus nidulans, and Aspergillus rugulosus, etc. ST may contaminate most of grains and forage grasses, and in particular severely contaminate wheat, maize, peanut, forage grasses. The basic structure of aflatoxin biosynthetic precursor ST consists of a difuran ring in connection with xanthone. The precursor has a structure similar to that of aflatoxin, and has toxicity that is second only to that of aflatoxin. Toxicity of ST includes hepatotoxicity, nephrotoxicity, cytogenetic toxicity and potent carcinogenicity. It enters into the human food chain after contaminating foods and feeds, and poses a threat to the health and safety of human. The hazard degree has a positive correlation with the intake of aflatoxin biosynthetic precursor ST. Since China is an area where there is more severe contamination with aflatoxin biosynthetic precursor ST, one of the key points to fortify the food safety is to improve detection of aflatoxin biosynthetic precursor ST in food products and feeds. Accordingly, it is necessary to determine the content of ST in cereals and finished products thereof suspected to be contaminated with the aflatoxin biosynthetic precursor ST.
Currently, methods for detecting aflatoxin biosynthetic precursor ST mainly include thin-layer chromatography (TLC) and liquid chromatography. TLC is easy to operate, and does not require complex and precise instrumentation, but has low sensitivity and low accuracy. Using TLC, a lower limit of detection of aflatoxin biosynthetic precursor ST in rice, maize, and wheat samples is 25 μg/kg and that in soybean and peanut samples is 50 μg/kg. In the recent years, high-performance liquid chromatography (HPLC) has been used widely in the detection of fungal toxins and has also been reported for detecting the aflatoxin biosynthetic precursor ST. However, the application of the HPLC in detection at the basic level has been limited by tedious pre-processing, expensive instrumentation, requirements for stringent operation environment, and professional operators, etc. Therefore, there is a pressing need in the detection field in China to study and develop novel techniques for rapid detection of aflatoxin biosynthetic precursor ST, which is of importance on guaranteeing the safety in food consumption in China.
Immunological analysis techniques have been increasingly the focus of rapid detection techniques for pollutants such as aflatoxin, due to advantages such as high sensitivity, short detection time, and easy to operate, etc. However, there are few reports on rapid detection techniques for aflatoxin biosynthetic precursor ST. Antigens and antibodies are the core reagents and the technological sources in immunological analysis techniques. The aflatoxin biosynthetic precursor ST has a molecular weight of 324, belongs to small molecule compounds (≦1000) and is incapable of directly stimulating an animal to produce antibodies. Only after covalently coupled to a carrier protein such as bovine serum protein (BSA), egg white albumin (OVA), and polylysine, etc., would aflatoxin be converted into a complete antigen with both reactogenicity and immunogenicity which can stimulate an animal to produce antibodies. Currently, antibodies obtained by immunization with an artificial antigen of aflatoxin biosynthetic precursor ST (the synthesis method is mainly sodium borohydride reduction) have been reported to be low in sensitivity and poor in specificity.